This invention relates generally to improvements in thermostatic mixing valve units and systems of the type generally shown and described in U.S. Pat. No. 5,350,112, for use with an emergency wash station, such as an eyewash station and/or a shower station. More specifically, this invention relates to an improved thermostatic mixing valve unit of substantially unitary or integrated construction having an internal high temperature limit valve for restricting hot water inflow upon a tempered water discharge exceeding a predetermined temperature level, in combination with a diverter valve for operating a cold water bypass valve to provide a substantial water discharge flow upon hot water restriction and/or failure of various system components.
Thermostatic mixing valves and related systems are generally known in the art for use in emergency wash stations such as eyewash and/or shower stations designed to provide a tempered water discharge outflow at a selected, and relatively lukewarm or tepid temperature level to flush contaminants such as hazardous chemicals and the like from a person's eyes, skin and clothing. A common system uses a thermostatic mixing valve for connection to cold and hot water supplies, and includes means for thermostatically and automatically blending or mixing these water inflows to produce a discharge outflow having the selected, tempered temperature.
In the past, tempered water mixing systems have on occasion encountered malfunction in the operation of the thermostatic mixing valve. Such malfunction can occur in any one of several different modes. As one example, the mixing valve can stick in a position providing unregulated water flow, wherein too much hot water can result in potential scalding of a person using the emergency wash station. In another failure mode, either one of a pair of hot and cold water check valves can stick in a closed position thereby preventing flow of hot or cold water to the mixing valve and resultant unregulated water temperature at the discharge outflow.
Some tempered water mixing systems have been designed with back-up features intended to address at least some of these potential failure modes. For example, solenoid operated valves have been used in combination with various temperature switches and/or flow rate switches to bypass cold water around the main mixing valve when a hot water malfunction occurs. Such devices rely, however, upon electrical power to achieve proper back-up operation. In the event of a power failure, the back-up devices have generally failed to function, or otherwise have provided for only cold water flow. In addition, during normal operation, the electrically operated components can cycle back-and-forth, so that a user is subjected to alternating brief flows of water that are either too hot or too cold. Further, electrically powered back-up devices are unsuitable for many industrial applications wherein the emergency wash station must be located in close proximity to volatile materials.
U.S. Pat. No. 5,350,112 discloses an improved tempered water mixing system wherein a high temperature limit thermostat is installed within the tempered water discharge outflow, and responds to detection of a tempered water temperature exceeding a predetermined limit by restricting hot water inflow to the main mixing valve. In addition, a cold water bypass valve responds to the pressure differential between a cold water inlet and the discharge outflow for bypassing cold water around the main mixing valve to maintain a substantial discharge outflow upon restriction and/or failure of the hot water inflow to the main mixing valve. However, this system as shown and described in U.S. Pat. No. 5,350,112 does not account for failure of the cold water inflow to the main mixing valve, as can occur upon sticking of a cold water check valve in a closed position.
There exists, therefore, a significant need for further improvements in and to thermostatic mixing valve units and systems of the type designed to provided a tempered water discharge outflow to an emergency wash station, such as to an eyewash station or the like. More particularly, there exists a need for a further improved thermostatic mixing valve unit designed to bypass cold water around a main mixing valve upon restriction and/or failure of either one of the cold and/or hot water supplies to the main mixing valve. The present invention fulfills this need and provides further related advantages.